1. Field on the Invention
The subject invention relates to an exhaust muffler for achieving an efficient flow pattern in a narrow space.
2. Description of the Prior Art
Prior art exhaust mufflers include a plurality of tubes disposed within an external shell. The external shell typically is divided into a plurality of chambers which communicate with at least selected tubes. The communication between the chambers and the tubes may be provided by perforations, louvers or cutouts in selected tubes. Other tubes may have an open end extending into a chamber to provide the necessary communication. The tubes, chambers and communication means are designed to attenuate most of the noise associated with the flowing exhaust gas without imposing excessive back pressure on the exhaust gas stream.
Tri-flow mufflers have an efficient flow pattern and are commonly used in the prior art. The prior art tri-flow muffler includes an inlet tube, a return tube and an outlet tube disposed in parallel relationship to one another. The inlet tube extends from the inlet end of the muffler to a first reversing chamber near the outlet end of the muffler. The return tube extends from the first reversing chamber to a second reversing chamber near the inlet end of the muffler. The outlet tube extends from the second reversing chamber to the outlet end of the muffler. The three parallel tubes in the typical prior art tri-flow muffler will pass through baffles which divide the prior art muffler into a plurality of chambers. Selected tubes may be perforated or louvered to enable gas communication between the tubes and the surrounding chamber. The relative dimensions of the tubes, the perforations and the chambers vary widely from one prior art tri-flow muffler to another in accordance with characteristics of the flowing exhaust gas. However, in most prior art tri-flow mufflers, the inlet tube, the return tube and the outlet tube will be of substantially the same cross-sectional dimensions to avoid unnecessary increases in back pressure.
Perforated tubes passing through expansion chambers often are not enough to attenuate all noise associated with the flowing exhaust gas, and in many cases at least one narrow range of low frequency noise will remain. These low frequency noises typically are attenuated by a tuning tube having one end communicating with the flowing exhaust gas and having the other end extending into a closed low frequency resonating chamber. The length and cross-sectional dimensions of the tuning tube and the volume of the low frequency resonating chamber are selected to attenuate a particular narrow range of low frequency noise.
Mufflers formed substantially from stamped components have been available for many years. Recent advances in stamped muffler technology have enabled acoustical tuning equal to or better than the acoustical performance of conventional mufflers. A particularly desireable and commercially acceptable stamp formed muffler is shown in U.S. Pat. No. Re. 33,370 which was reissued on Oct. 9, 1990. A very effective muffler formed substantially from stamped components and having a flow pattern resembling a conventional tri-flow muffler is shown in copending application Ser. No. 866,753, now U.S. Pat. No. 5,252,788, which was filed on Apr. 10, 1992.
Exhaust system design is complicated by the limited available space on the underside of a vehicle. In this regard, typical tri-flow mufflers have the inlet tube, the return tube and the outlet tube disposed in a common plane so that the muffler can assume a generally oval cross-section, with the major axis of the oval aligned generally horizontally on the underside of the vehicle. Although tube dimensions will vary from muffler to muffler, a typical prior art muffler may have flow tubes with an inside diameter of approximately 2.50 inches. Three such tubes have combined outside diameters in excess of eight inches. However, the tubes must be spaced from one another and spaced from the shell of the muffler to enable adequate support by the baffles. Hence, a typical prior art tri-flow muffler formed from conventional components may have a width of approximately 11.50 inches.
Stamp formed mufflers achieve several performance and manufacturing efficiencies, but normally do not enable smaller size mufflers. In particular, generally planar lands about one inch wide are defined between adjacent stamp formed tubes and between the tubes and peripheral flanges of prior art stamp formed mufflers. Hence, a prior art stamp formed tri-flow muffler also will require a width of approximately 11.50-12.00 inch. The limited space on the underside of many vehicles cannot readily accommodate prior art tri-flow mufflers of these dimensions. Hence, engineers occasionally have been forced to use a plurality of mufflers disposed in parallel or in series. Although each muffler in such an exhaust system may be smaller, the overall system is likely to be substantially more expensive. These problems may be even greater in exhaust systems having two exhaust pipes leading into a single muffler.
The back pressure referred to above affects performance of an engine. Hence, engine performance and efficiency can be improved by lowering back pressure. Larger exhaust pipes generally produce less back pressure. However, the flow tubes within a muffler generally must match the cross-sectional dimensions of the exhaust pipe leading into the muffler. Prior art mufflers with larger flow tubes necessarily would occupy a larger space envelope. Hence, attempts to improve performance by lowering back pressure have been feasible only on vehicles with sufficient space to accommodate larger prior art mufflers.
In view of the above, it is an object of the subject invention to provide an exhaust muffler that is well suited to narrow space envelopes.
Another object of the subject invention is to provide a muffler having relatively large cross-section pipes for a limited space envelope with a limited width.
A further object of the subject invention is to provide a tri-flow muffler formed substantially from stamped components.
Yet another object of the subject invention is to provide a tri-flow muffler that is well suited for relatively narrow space envelopes.